This application claims the priority of German Patent Document 100 62 350.6, filed Dec. 14, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method and apparatus for controlling a supercharging device for an internal combustion engine, especially in a motor vehicle.
A known system for controlling the boost pressure of an internal combustion engine with an exhaust turbocharger is described in German patent specification DE 39 43 010 C2. To regulate boost pressure, a blow-off valve is opened or closed according to a duty cycle of a trigger signal. In stable driving conditions, a duty cycle is taken from a table in which duty cycle values are listed in relation to the actual intake line pressure and engine speed. In this manner, the boost pressure can be kept at a maximum permissible pressure limit. If the permissible pressure limit is exceeded during partial-load operation, the base duty cycle is corrected with the aid of a proportional and integral (PI) controller in order to return the intake line pressure to a value below the pressure limit. During full load operation, the base duty cycle is also corrected with the aid of the PI controller, in order to keep the intake line pressure close to the pressure limit. During full load operation, this type of PI controller operation only takes place when, on the one hand, the intake line pressure falls within a range surrounding the pressure limit and, on the other hand, a local maximum intake line pressure was exceeded and the intake line pressure gradient is therefore less than zero. Accordingly, strong surges in supercharging pressure during the acceleration of a vehicle is avoided because an integral (I) controller is only activated after a local intake line pressure maximum is exceeded and when the intake line pressure is already approaching the pressure limit.
German disclosure document DE 198 01 395 A1 discloses a device for controlling boost pressure in an exhaust gas turbocharger with a variably adjustable turbine geometry. In this device, the air mass flow in the suction pipe, in an initial low load and/or RPM range, is used as a control variable for the exhaust gas re-circulation control device. In a second, higher load and/or RPM range, the boost pressure in the suction pipe is used as the control variable. The control device may be provided with a single controller in which the control variable is switched between the air mass flow and the boost pressure.
The invention relates to a method and apparatus for controlling a supercharging device with which an improved dynamic and an improved quality of control are achieved for all types of exhaust gas turbochargers.
To this end, a method is provided, according to the present invention, for controlling a supercharging device for an internal combustion engine, especially an exhaust gas turbocharger for a diesel engine of a motor vehicle, in which a range of control is divided into at least four sub-ranges, each having different control characteristics, depending on a gradient of the variable being controlled and a difference between the variable being controlled and a control variable. As a result of these measures, an improved dynamic and improved quality of control can be attained by adjusting the control characteristic to conform to a given condition of operation. If the control difference is constant but the gradients are variable, various control segments can be set and a variable control characteristic can be achieved. The control variable or the set value can be derived from a characteristic field, such as a set value plotted against load and engine speed for boost pressure, or an air mass flow plotted against the desired injection volume and the engine speed. An exhaust gas turbocharger with variable turbine geometry, the settings of which are adjusted, can be provided as a supercharging device.
In a further embodiment of the invention, it is provided that the sub-ranges are subdivided according to a positive or negative difference between the variable being controlled and the control variable, and according to a positive or negative gradient of the variable being controlled. As a result of these measures, the range of control is divided into four sub-ranges or four quadrants, with a subdivision of this nature being especially suitable for controlling a supercharging device of an internal combustion engine. Thus, aggressive control parameters are preferably used with positive gradients of the variable being controlled, so that a high dynamic is achieved with increases in the variable being controlled, such as the boost pressure. On the other hand, defensive control parameters are used with negative gradients of the variable being controlled, so that, for example, undershooting at decreasing boost pressure can be avoided and a high quality of control can be attained. In contrast to conventional controllers, this not only makes allowances for the difference between the variable being controlled and the control input or the set value, but also for the dynamic behavior of the variable being controlled. In this manner, the variable being controlled can be adjusted more quickly to a predetermined set value without running the risk of significant overshoot or undershoot. If, for example, a PI controller is provided, two characteristic fields can be provided for each quadrant, in which fields the P component and/or the I component is stored as a factor of the gradient of the variable being controlled and the control difference.
In a further embodiment of the invention, the control characteristic is determined by proportionally acting and integrating controller components and, in the case of negative gradients of the variable being controlled, a stronger emphasis is placed on the controller components with integrating action. As a result of these measures, undershooting at negative gradients of the variable being controlled is avoided and/or the variable being controlled is gradually brought closer to the reference variable.
In a further embodiment of the invention, it is provided that the control characteristic is determined by proportionally acting and integrating controller components and, in the case of positive gradients of the variable being controlled, that a stronger emphasis is placed on the proportionally acting controller components. As a result of these measures, a high dynamic can be achieved at boost pressure below the set value and minor overshooting at boost pressure above the set value when the gradients of the variable being controlled are positive, such as in the case of increasing boost pressure, by quickly returning the boost pressure to the set value.
In a further embodiment of the invention, it is provided that controller components with integrating action are only activated to the control characteristic once the variable being controlled has almost reached the control variable, falling within a predetermined range around the control variable. As a result of these measures, a high dynamic and rapid approaching of the control variable is achieved, as controller components with integrating action are only activated when the variable being controlled has almost reached the control variable. On the other hand, a high quality of control is achieved, especially within a predetermined range around the control variable, as the controller components with integrating action then provide for precise adjustment of the set value.
In a further embodiment of the invention, a default value of the supercharging device and a correction of the default value, which are subject to the actual fuel injection volume, are provided. Such a correction of the default value is especially advantageous in a diesel engine. To limit exhaust smoke during full load acceleration from low engine speeds, the fuel injection volume must be restricted, thus preventing the available fuel injection volume from providing the necessary exhaust gas energy. As a result of the dynamic correction of the default value, the settings for the control variables of the supercharging device are corrected in the direction of an increase in exhaust gas energy. The advantage of providing a dynamic correction of the default value instead of applying aggressive control parameters is that there is no risk of overshoot, as the control characteristic does not have to be designed for an increase in exhaust gas energy, even in the sub-range in question. An outcome of the corrected default value is linked to an outcome of the control procedure.
In a further embodiment of the invention, it is provided that an air mass flow in the suction path is used as control variable. The use of an air mass flow as control variable, i.e., of one air mass per stroke or crank disk segment, offers various advantages during operation of an internal combustion engine. For example, only one control variable is needed for the entire range of operation, i.e., both operation with exhaust gas re-circulation and supercharging operation, because a predetermined set value is provided on the basis of the air mass flow across the entire range of operation. A predetermined set value can be provided by a single characteristic field for operation with exhaust gas re-circulation and for supercharging operation, in that the air mass flow is applied as a function of the desired injection volume and engine speed. In contrast to boost pressure, the air mass flow provides more information, especially when the intake channels become clogged with dirt, and precisely reflects the filling of the cylinders, regardless of suction pipe temperature and atmospheric pressure. The air mass flow is measured with an air mass gauge. In contrast to the measurement of boost pressure, where suction tube temperature must be taken into account, only one sensor is required to measure air mass flow, thus reducing the impact of sensor errors.
In a further embodiment of the invention, it is provided that a set value of the air mass flow is limited by a characteristic field of the maximum allowable air mass flow, in which the maximum allowable air mass flow is stored as a function of the engine speed and the supercharging air temperature. As a result of these measures, engine protection can be achieved by limiting the maximum allowable combustion chamber pressure.
In a further embodiment of the invention, it is provided that an exhaust gas turbocharger is provided as a supercharging device, and that a set value of the control variable is verified using a limiting characteristic curve of the maximum allowable compression ratio of the exhaust gas turbocharger. These measures enable the turbocharger to be protected against overspeed and pumping operation.
In a further embodiment of the invention, it is provided that an exhaust gas turbocharger is provided as a supercharging device, and that, to detect unstable operating points of the exhaust gas turbocharger, fluctuations in supercharging pressure and/or in air mass flow in the suction path are recorded and analyzed and, in the event of detection of an unstable state, the maximum allowable compression ratio of the exhaust gas turbocharger is reduced. In this manner, the turbocharger can be protected against pumping operation, i.e., unstable operation. If an air column in the suction path begins to vibrate, the share of the resonant frequency of the air column increases. If the amplitude of the resonant frequency exceeds a predetermined value, pumping operation is present, and the maximum allowable compression ratio does not have to be reduced as drastically to remove the exhaust gas turbocharger from unstable operation.
In accordance with another aspect of the invention, an apparatus for controlling a supercharging device for an internal combustion engine includes a controller that has a range of control. The range of control includes at least four sub-ranges that are divided in accordance with a gradient (dx/dt) of the variable to be controlled (x) and a difference (xcex94x) between the variable to be controlled (x) and a control variable (xs).
In accordance with a further aspect of the invention, a method for controlling a supercharging device for an internal combustion engine includes (1) dividing a range of control into at least four sub-ranges in accordance with a gradient (dx/dt) of the variable to be controlled (x) and a difference (xcex94x) between the variable to be controlled (x) and a control variable (xs), and (2) controlling a variable (x) using different control characteristics in each of the at least four sub-ranges.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.